Q.The number and kinds of organism is not constant. How do you explain this statement?

The number and kinds of organisms are not constant because life on the planet is not a fixed, finished catalogue.

• Even today, only a portion of all existing organisms — an estimated 1.7 to 1.8 million species — has actually been formally identified and described, so new species are continually being discovered and added to the known total.
• The living world also keeps changing over time, as populations diverge, new forms arise and others disappear, so the actual number and variety of organisms present is never truly static. …

It might seem, at first, that the living world could eventually be catalogued completely and the count of species fixed once and for all. In practice this is not so, for two related reasons.

• Discovery is incomplete. Only around 1.7 to 1.8 million species have so far been formally recognised and described, out of a far larger — and still uncertain — total that actually exists. Every newly explored habitat, from a dense forest to a previously unstudied region, tends to reveal organisms that were not previously known, adding to the recorded total.
• Life itself is not static. The organisms present in any given place and time are the product of an ongoing biological process, not a permanent, unchanging list — populations change, some forms persist while others do not, and the composition of living diversity shifts accordingly. …